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Global maize production, utilization, and consumption

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Maize (Zea mays), also called corn, is believed to have originated in central Mexico 7000 years ago from a wild grass, and Native Americans transformed maize into a better source of food. Maize contains approximately 72% starch, 10% protein, and 4% fat, supplying an energy density of 365 Kcal/100 g and is grown throughout the world, with the United States, China, and Brazil being the top three maize-producing countries in the world, producing approximately 563 of the 717 million metric tons/year. Maize can be processed into a variety of food and industrial products, including starch, sweeteners, oil, beverages, glue, industrial alcohol, and fuel ethanol. In the last 10 years, the use of maize for fuel production significantly increased, accounting for approximately 40% of the maize production in the United States. As the ethanol industry absorbs a larger share of the maize crop, higher prices for maize will intensify demand competition and could affect maize prices for animal and human consumption. Low production costs, along with the high consumption of maize flour and cornmeal, especially where micronutrient deficiencies are common public health problems, make this food staple an ideal food vehicle for fortification.
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Ann. N.Y. Acad. Sci. ISSN 0077-8923
ANNALS OF THE NEW YORK ACADEMY OF SCIENCES
Issue:
Technical Considerations for Maize Flour and Corn Meal Fortification in Public Health
Global maize production, utilization, and consumption
Peter Ranum,1Juan Pablo Pe ˜
na-Rosas,2and Maria Nieves Garcia-Casal3
1Independent consultant, Tucson, Arizona. 2Evidence and Programme Guidance Unit, Department of Nutrition for Health and
Development, World Health Organization, Geneva, Switzerland. 3Laboratory of Pathophysiology, Center for Experimental
Medicine, Venezuelan Institute for Scientific Research, Caracas, Venezuela
Address for correspondence: Maria Nieves Garcia-Casal, Laboratory of Pathophysiology, Center for Experimental Medicine,
Venezuelan Institute for Scientific Research, Carretera Panamericana Km 11, Caracas 1020-A, Venezuela.
mngarciacasal@gmail.com
Maize (Zea mays), also called corn, is believed to have originated in central Mexico 7000 years ago from a wild grass,
and Native Americans transformed maize into a better source of food. Maize containsapproximately 72% starch, 10%
protein, and 4% fat, supplying an energy density of 365 Kcal/100 g and is grown throughout the world, with the United
States, China, and Brazil being the top three maize-producing countries in the world, producing approximately 563
of the 717 million metric tons/year. Maize can be processed into a variety of food and industrial products, including
starch, sweeteners, oil, beverages, glue, industrial alcohol, and fuel ethanol. In the last 10 years, the use of maize for
fuel production significantly increased, accounting for approximately 40% of the maize production in the United
States. As the ethanol industry absorbs a larger share of the maize crop, higher prices for maize will intensify demand
competition and could affect maize prices for animal and human consumption. Low production costs, along with
the high consumption of maize flour and cornmeal, especially where micronutrient deficiencies are common public
health problems, make this food staple an ideal food vehicle for fortification.
Keywords: maize; corn; production; consumption; varieties
Introduction
Cereal grains are the fruits of cultivated grasses. They
provide humankind with more nourishment than
any other food class and nearly half of the total
caloric requirement. While there are about a dozen
cereal crops used for food, only wheat, maize, and
rice are important human food sources, accounting
for 94% of all cereal consumption.1The consump-
tion of these cereals varies widely by region; wheat is
the preferred cereal in Central Asia, the Middle East,
South and North America, and Europe. Rice is the
major cereal in Asia, while maize (also referred to as
corn) is preferred in Southern and Eastern Africa,
Central America, and Mexico.
The way in which maize is processed and con-
sumed varies greatly from country to country, with
maize flour and meal being two of the most popular
products.2
The actual human consumption of these cere-
als is somewhat lower than the estimated figures
because of waste, use in nonfood products, and
because milling removes some of the outer layers, or
bran, which is generally used as animal feed. As with
all cereals, most micronutrients are concentrated in
the outer layers of the maize grain; thus, removing
these layers in the milling process results in the loss
of most vitamins and minerals.2,3
Consumption can be better estimated by adjust-
ing the values of cereal crops used for food and
human food sources by considering the extraction
rate (i.e., the proportion of flour or meal produced
from the whole-grain cereal). In most countries,
the extraction rate for maize varies from 60% to
100% depending on the product. The range for yel-
low maize goods is 60–65% in the United States.
Higher extraction rate levels are found in other
countries. In South Africa, for example, the ex-
traction rates for super, sifted, and unsifted maize
are 62%, 79–89%, and 99%, respectively.4Newly
developed maize varieties with a very short grow-
ing season produce a softer, smaller kernel of white
maize. These varieties (smaller and softer) can also
cause tremendous problems in the milling process,
doi: 10.1111/nyas.12396
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Maize production, utilization, and consumption Ranum
et al.
leading to a poor extraction rate.5The changes in
nutritional profile (ash, fat, and fiber content) at
the lower extraction rates will be less than those ob-
served at the higher extraction levels, as in the case of
wheat.6,7
Maize contains about 72% starch, 10% pro-
tein, and 4% fat, supplying an energy density of
365 Kcal/100 g,8as compared to rice and wheat, but
has lower protein content. Maize provides many of
the B vitamins and essential minerals along with
fiber, but lacks some other nutrients, such as vita-
min B12 and vitamin C, and is, in general, a poor
source of calcium, folate, and iron. Iron absorption,
particularly the nonheme iron present in maize, can
be inhibited by some components or foods in the
diet, such as vegetables, tea (e.g., oxalates), coffee
(e.g., polyphenols), eggs (e.g., phosvitin), and milk
(e.g., calcium).6,8 In countries where anemia and
iron deficiency are considered moderate or severe
public health problems, the fortification of maize
flour and cornmeal with iron and other vitamins
and minerals has been used to improve micronutri-
ent intake and prevent iron deficiency.9
History of maize
In the Western world, the term maize is used in-
terchangeably with corn. The reason for this is that
all grains were called corn under early British and
American trade and the name was retained for
maize because it was the most common grain in
commerce. Although the origin of the word maize
is also controversial, it is generally accepted that
the word has its origin in Arawac tribes of the in-
digenous people of the Caribbean. On the basis of
this common name, Linnaeus included the name
as species epithet in the botanical classification Zea
(Zea mays L.).10
It is considered that maize was one of the first
plants cultivated by farmers between 7000 and
10,000 years ago, with evidence of maize as food
coming from some archaeological sites in Mexico
where some small corn cobs, estimated at more than
5000 years old, were found in caves. The discovery
of fossil pollen and cave corncobs in archaeological
areas support the position that maize originated in
Mexico.Other theories descr ibe maize as originating
in the region of the Himalayas in Asia, the product of
a cross between Coix spp. and some Andropogoneas
(probably of the Sorghum species), both parental
chromosomes with five pairs, or in the high An-
des of Bolivia, Ecuador, and Peru, as evidenced by
the presence of popcorn in South America and the
wide genetic diversity present in the Andean maize,
especially in the highlands of Peru.10,11
Biological and archaeological approaches to de-
termine where and when maize was initially do-
mesticated continue to evolve through the use of
genetic research and complex methodologies.12,13
Some authors consider maize to have started from
a wild grass, called teosinte, which is quite differ-
ent from the maize of today, while others suggest
the formation of a hybrid of two wild grasses—a
perennial subspecies of teosinte (Zea diploperennis)
and a species of Tripsacum. By systematically col-
lecting and cultivating plants best suited for human
consumption, Native Americans transformed maize
over a couple 1000 years to a plant with larger cobs
and more rows of kernels, making it a better source
of food.13 This provided enough food for the bulk
of their diet for an entire year, allowing people to
live in one location for an extended period of time.
Thespreadofmaizefromitscenteroforiginin
Mexico to various parts of the world has been re-
markable and rapid with respect to its evolution as
acultivatedplantandasavarietyoffoodproducts.
The inhabitants of several indigenous tribes in Cen-
tral America and Mexico brought the plant to other
regions of Latin America, the Caribbean, and then to
the United States and Canada. European explorers
took maize to Europe and later traders took maize
to Asia and Africa.14–16
One limitation with maize is that while it con-
tains the vitamin niacin, it is in a bound form that
is not readily available to the body. It is also low in
tryptophan, a niacin precursor. In order for niacin
to be released from the bound form, it needs to have
the pH increased before entering the low pH of the
stomach. Early natives in Latin America stumbled
upon a process, called nixtamalization, which in-
volved soaking the whole maize in a lime solution
(calcium hydroxide), followed by grinding to pro-
duce a paste, called masa, from which tortillas are
made.17 This process had two benefits: it converted
the hard maize kernels into a more digestible form
and released the bound niacin. Without this pro-
cess there would have been much higher incidences
of pellagra due to niacin deficiency.18 In Europe,
North America, and Africa, where the nixtamaliza-
tion process was not used, pellagra became a prob-
lem in some areas. One of the real success stories
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Ranum
et al.
Maize production, utilization, and consumption
of cereal fortification was the addition of niacin to
maize meal beginning in 1941, which contributed to
the elimination of pellagra as a major health prob-
lem in the Southeastern United States. Pellagra was
not a public health problem in other parts of the
world, perhaps because they had a more varied diet
that provided sufficient amounts of niacin.19
Types of maize
Different types of maize are grown throughout the
world, with one important difference being color.
Maize kernels can be different colors ranging from
white to yellow to red to black. Most of the maize
grown in the United States is yellow, whereas people
in Africa, Central America, and the southern United
States prefer white maize. Yellow maize is not popu-
lar in Africa for reasons associated with the percep-
tion of social status: apparently it is associated with
food-aid programs and is perceived as being con-
sumed only by poor people. Also, the feed industry
consumes mostly yellow maize in the manufacture
of animal feed.4But the main reason for the pref-
erence for white maize is simply one of tradition:
people are used to eating a white product in these
countries, usually the whiter the better. This prefer-
ence means a lower consumption of -carotene and
-cryptoxanthin, vitamin A precursors, present in
higher concentrations in yellow and orange maize.
This also shows up in the preference for meal and
flour made with higher extraction rates, which are
whiter than the whole-grain products, but also with
lower contents of fiber, vitamins, and minerals.20
The quality of white maize is important since it af-
fects the milling performance, grading, and yield of
high-quality products.
There is a classification of maize on the basis of the
size and composition of the endosperm, resulting in
an artificial definition by kernel type as follows: dent,
flint, waxy, flour, sweet, pop, Indian, and pod corn.
Another difference or classification criterion is the
sweetness or amount of sugar. The amount of resid-
ual sugar depends on the variety of maize and when
it is harvested from the field. Sweet maize stores
poorly and must be eaten fresh, canned, or frozen
before the kernels age, becoming small, tough, and
starchy. Sweet varieties cannot be fortified.15,16
Genetically modified (GM) herbicide-resistant
maize (e.g., Bt corn, a variant of maize that has
been genetically altered to express one or more pro-
teins from the bacteria, Bacillus thuringeiensis)has
become the major type of maize grown in many
countries, including the United States where 85%
of the crop is GM. European and African countries
originally banned GM maize, but while still very
controversial, this position may be changing as the
benefits of Bt corn become accepted. In fact, as of
2011, herbicide-resistant GM maize was grown in
14 countries.21 By 2012, 26 varieties of herbicide-
resistant GM maize were authorized for import into
the European Union,22 and in 2012, the European
Union was reported to import 30 million tons of GM
crops. The GM maize MON810 was cultivated on
almost 89,000 hectares in five European countries,
particularly in regions with high infestation levels
of maize borer (a pest affecting both the quality and
quantity of the harvest).22
There does not appear to be any nutritional differ-
ence with Bt maize; therefore, its presence or absence
should have no effect on fortification technology
or policy.23–26 Other recent papers address maize
milling and the different types of milled products
made from maize. The main products, all of which
can and are being fortified, are meal, flour, pre-
cooked meal, dry masa or hominy flour, and break-
fast cereals. In addition, there are mixtures with
other ingredients, such as Corn Soy Blend, used for
infant and food-aid feeding. Some products, such
as corn chips and masa dough, may not be suitable
for fortification.6
Maize production, utilization,
and economics
Maize is grown throughout the world, although
there are large differences in yields (Table 1). The
Food and Agriculture Organization (FAO) of the
United Nations indices of agricultural production
include commodities that are considered edible and
contain nutrients, and show the relative level of
the aggregate volume of agricultural production
for each year in comparison with the base period
1999–2001. It is estimated that in 2012, the total
world production of maize was 875,226,630 tons,27
with the United States, China, and Brazil harvesting
31%, 24%, and 8% of the total production of maize,
respectively.
Food balance sheets developed by the FAO are
commonly used as a data source for estimating pat-
terns, levels, and trends of national diets, and are
referred to as the FAOSTAT food balance sheets,
in reference to the database that gathers the data.
107
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Maize production, utilization, and consumption Ranum
et al.
Tab le 1. Corn production in 2012 by country,
FAOSTAT27
Country
Maize production in 2011
(million MT/year)
United States of America 274
China 208
Brazil 71
Mexico 22
Argentina 21
India 21
Ukraine 21
Indonesia 19
France 16
Canada 12
South Africa 12
It presents a comprehensive picture of the pattern
of a country’s food supply during a specified ref-
erence period. The FAOSTAT food balance sheets
show maize availability for human consumption,
which corresponds to the sources of supply and its
utilization. The total quantity of maize produced in
a country added to the total quantity imported and
adjusted to any change in stocks that may have oc-
curred since the beginning of the reference period
gives the supply available during that period. On the
utilization side, a distinction is made between the
quantities of maize exported, fed to livestock and
used for seed, losses during storage and transporta-
tion, and supplies available for human consump-
tion. The per capita supply of maize available for
human consumption is then obtained by dividing
the respective quantity by the related data on the
population actually partaking in it. Data on per
capita maize supply are expressed with respect to
quantity and by applying appropriate food compo-
sition factors for maize, including dietary energy
value, protein, and fat content.27 Owing to the low
cost and high accessibility of FAOSTAT food bal-
ance sheet data, they have historically been the main
data source of food fortification program design–
related information. However, their ability to iden-
tify potentially fortifiable or already fortified foods
is constrained by the fact that the data are lim-
ited to maize as a primary commodity and do not
capture processed potential vehicles, such as maize
flour and cornmeal, or distinguish the proportion of
these items consumed that are purchased.28 Also, the
national-level data from FAO food balance sheets do
not provide any information on food consumption
by individuals or populations.29
Maize data reported in FAOSTAT food balance
sheets are reported at the farm-level with respect
to grains. Although of interest for a maize flour
fortification program, the FAOSTAT food balance
sheet does not report data on the amount of maize
flour available for consumption and the data must
be calculated manually. In order to calculate the
amount of flour available for consumption (and the
daily g/capita availability) in a country, the extrac-
tion rate reported by the milling industry is applied.
For maize flour, the extraction rate varies in differ-
ent countries depending on the type of flour. Some
procedures have been established to estimate food
balance sheet data for maize flour and cornmeal; al-
though these procedures are not discussed explicitly
in the Food Balance Sheet Handbook, they would
follow the same protocol outlined for wheat flour
data.28
An important part of maize production is being
used to generate ethanol fuel (ethyl alcohol), the
same type of alcohol found in alcoholic beverages.
It is most often used as a motor fuel, mainly as a bio-
fuel additive for gasoline. Maize is the primary feed-
stuff used to produce ethanol. Strong demand for
ethanol production has resulted in increased maize
prices and has provided incentives to increase maize
acreage. There are various social, economic, envi-
ronmental, and technical issues with biofuel pro-
duction and use, including the effect of moderating
oilpricesandthe“foodversusfuel”debate.
30
Both maize dry-milling and wet-milling methods
of producing ethanol generate a variety of econom-
ically valuable coproducts, the most prominent of
which is distillers’ dried grains with solubles, which
can be used as a feed ingredient for livestock.
The United States is the world’s largest producer
of maize and dominates world maize trade. Ex-
ports account for a relatively small portion of de-
mand for U.S. maize—approximately 15%. Experts
consider that the low demand for exports means
that maize prices are largely determined by sup-
ply and demand relationships in the U.S. mar-
ket, and the rest of the world usually adjusts to
prevailing U.S. prices. The large influence of U.S.
maize supply makes world maize trade. Argen-
tine farmers plant their maize after discovering the
size of the U.S. crop, thereby providing a quick,
108 Ann. N.Y. Acad. Sci. 1312 (2014) 105–112 C2014 New York Academy of Sciences.
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Ranum
et al.
Maize production, utilization, and consumption
Tab le 2 . Domestic corn use in the United States from 1980 to 2013 in billion of bushels
Corn use 1980 1990 2000 2010 2013
Animal feed and residual 4.16 4.75 5.73 4.79 5.00
Food, seed, and industrial 0.81 1.08 1.15 1.25 1.46
Ethanol production 0.02 0.42 0.83 5.00 5.00
Total 4.99 6.25 7.71 11.04 11.46
Source: Adapted from the United States Department of Agriculture (USDA).31
market-oriented supply response to short U.S.
crops. Several countries, including Brazil, Ukraine,
Romania, and South Africa, have had significant
maize exports when crops were large or interna-
tional prices were attractive.31 China has been a
significant source of uncertainty in world maize
trade, swinging from being the second largest ex-
porter in some years to occasionally importing
significant quantities. China’s maize exports are
largely a function of government export subsidies
and tax rebates, because the prices in China are
mostly higher than those in the world market.
While a large maize producer, Mexico processes
much of its production of white maize into human
food products, but has turned to imported yellow
maize for livestock feed to support increased meat
production.31
The analysis of the use of maize in the United
States for the last 30 years shows that it has been used
mainly for animal feeding, followed by human con-
sumption and alcohol production (Table 2). How-
ever, in the last 10 years, the use of maize for fuel
production significantly increased.32 As the ethanol
industry absorbs a larger share of the maize crop,
higher prices for maize will intensify demand com-
petition among domestic industries and external
buyers. This could also affect maize prices for ani-
mal and human consumption, although maize has
historically been one of the least expensive foods and
food ingredient available. It is estimated that nearly
40% has been used in recent years to make ethanol
for fuel. Of this, 27% becomes ethanol and 12% is
the distillers’ dry grain residue that goes to animal
feed, making the total animal feed use at 50%.32 Ex-
ports accounted for 13% and 4% are used to make
high-glucose corn syrup. Part of the remaining 7% is
used to make corn oil, cornstarch, corn syrups, and
other industrial applications, while some is used to
make whiskey and other alcoholic beverages.
Maize consumption by country and World
Health Organization region
Estimated maize consumption in grams per person
per day in countries where maize is considered an
important food source (i.e., above 50 g/person/day)
were corrected for an average 80% extraction rate,
using the FAOSTAT food balance sheets with 2009
data by World Health Organization (WHO) re-
gion (Table 3). It is clear that maize is a staple in
the African region where the consumption ranges
from 52 to 328 g/person/day and the region of
the Americas where the highest consumption was
267 g/person/day in Mexico. The results may vary
according to the extraction rate, which varies in each
countrybytypeofflourmilledaswellasbythemaize
type used. No consumption above 50 g/person/day
was estimated in the Western Pacific Region.
Other data sources to estimate maize flour con-
sumption have been proposed. Household Con-
sumption and Expenditures Surveys, which include
Household Income and Expenditure Surveys, Liv-
ing Standards Monitoring Surveys, and National
Household Budget Surveys, can help to address the
food consumption information gap. Some coun-
tries such as Zambia have introduced specific food
item categories in order to be able to obtain more
precise data with which to assess the feasibility of
or to design fortification programs. In 2006, the
Zambia Living Standards Measurement Study asked
about households’ consumption of maize with a fo-
cus on breakfast mealie meal, roller mealie meal, and
hammer-milled meal, in addition to maize grain, in
order to be able to distinguish those maize meal
consumers who purchase their product from large-
scale, modern roller mills.29
Major importers of maize in 2009 were Japan,
South Korea, and Mexico.27 Experts from the U.S.
Department of Agriculture31 consider Japan, while
producing almost no coarse grains, to be a very large
109
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Maize production, utilization, and consumption Ranum
et al.
Tab le 3 . Countries with the highest maize consumption
(g/person/day) by WHO region
WHO region Country
Maize consumption
(g/person/day)
African region Lesotho 328
Malawi 293
Zambia 243
Zimbabwe 241
South Africa 222
Kenya 171
Togo 160
Swaziland 152
Tanzania 128
Namibia 127
Benin 119
Mozambique 116
Burkina Faso 107
Ethiopia 94
Angola 81
Botswana 78
Cameroon 75
Cape Verde 72
Central
African
Republic
71
Mali 70
Seychelles 69
Senegal 62
Nigeria 60
Ghana 53
Uganda 52
Region of the Mexico 267
Americas Guatemala 187
Honduras 169
El Salvador 157
Nicaragua 148
Venezuela 135
Paraguay 121
Colombia 92
Bolivia 86
Cuba 66
Uruguay 63
Belize 61
Brazil 55
Panama 53
Haiti 50
Southeast Asia Timor-Leste 190
region Nepal 98
Continued
Tab le 3 . Continued
WHO region Country
Maize consumption
(g/person/day)
Korea, DPR 93
Morocco 84
Indonesia 79
European region Bosnia and
Herzegovina
181
Romania 85
Slovenia 75
Israel 64
Macedonia 59
Kyr gy zstan 5 8
Eastern
Mediterranean
region
Egypt 127
Note: Estimated at 80% extraction from 3-year average
(2007–2009) FAOSTAT1data.
meat producer; therefore, the country is a steady
buyer of maize, with attention to quality. In recent
years, Japanese imports of maize for livestock feed
have declined, while imports for industrial use and
starch manufacturing have increased. South Korea,
the second largest importer of maize in the world, is
price conscious and willing to buy maize from the
cheapest source or switch to wheat or other grains.
Mexico is a growing importer.
World production of maize has shown a slight but
steady increase over the years, but human consump-
tion of the grain has remained steady. It is thought
that the majority of the increase in production has
corresponded to an increase in the use of maize for
animal feed. However, maize is still a staple food for
many people, especially in Africa.
Maize has food, feed, and industrial uses. It is
a major component of livestock feed. The amount
of maize used for feed also depends on the crop’s
supply and price, the amount of supplemental in-
gredients used in feed rations, and the supplies and
prices of competing ingredients.
Acknowledgments
This work received financial support from the De-
partment of Nutrition for Health and Development,
Evidence and Programme Guidance Unit, WHO
(Geneva, Switzerland). WHO thanks the Interna-
tional Micronutrient Malnutrition Prevention and
110 Ann. N.Y. Acad. Sci. 1312 (2014) 105–112 C2014 New York Academy of Sciences.
The World Health Organization retains copyright and all other rights in the manuscript of this article as submitted for publication.
Ranum
et al.
Maize production, utilization, and consumption
Control (IMMPaCt) Program of the Centers for Dis-
ease Control and Prevention (CDC; Atlanta) for fi-
nancial support for this work. This manuscript was
presented at the WHO consultation “Technical Con-
siderations for Maize Flour and Corn Meal Fortifi-
cation in Public Health” in collaboration with the
Sackler Institute for Nutrition Science at the New
York Academy of Sciences and the Flour Fortifica-
tion Initiative (FFI), convened on April 8 and 9,
2013, at the New York Academy of Sciences in New
York. This article is being published individually,
but will be consolidated with other manuscripts as
aspecialissueofAnnals of the New York Academy of
Sciences, the coordinators of which were Drs. Maria
Nieves Garcia-Casal, Mireille McLean, Helena Pa-
chon, and Juan Pablo Pe˜
na-Rosas. The special is-
sue is the responsibility of the editorial staff of An-
nals of the New York Academy of Sciences, who del-
egated to the coordinators preliminary supervision
of both technical conformity to the publishing re-
quirements of Annals of the New York Academy of
Sciences and general oversight of the scientific merit
of each article. The workshop was supported by the
Sackler Institute for Nutrition Science at the New
York Academy of Sciences and the FFI. The authors
alone are responsible for the views expressed in this
article; they do not necessarily represent the views,
decisions, or policies of the institutions with which
they are affiliated or the decisions, policies, or views
of the WHO. The opinions expressed in this publica-
tion are those of the authors and are not attributable
to the sponsors, publisher, or editorial staff of Annals
of the New York Academy of Sciences.
Conflicts of interest
The authors declare no conflicts of interest.
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Accelerator mass spectrometry age determinations of maize cobs (Zea mays L.) from Guilá Naquitz Cave in Oaxaca, Mexico, produced dates of 5,400 carbon-14 years before the present (about 6,250 calendar years ago), making those cobs the oldest in the Americas. Macrofossils and phytoliths characteristic of wild and domesticated Zea fruits are absent from older strata from the site, although Zea pollen has previously been identified from those levels. These results, together with the modern geographical distribution of wild Zea mays, suggest that the cultural practices that led to Zea domestication probably occurred elsewhere in Mexico. Guilá Naquitz Cave has now yielded the earliest macrofossil evidence for the domestication of two major American crop plants, squash (Cucurbita pepo) and maize.